Gram quantities of highly-purified human thrombin preparations are being produced to enable investigations on the structures, enzymic specificities, and potential physiologic importance of human alpha-thrombin and its derivative forms beta- and gamma-thrombins. Current projects in this laboratory are: 1) continual production of human alpha-thrombin as well as gamma-thrombin and by-products (e.g., prothrombin fragments, prothrombin complex fractions); 2) refinement of methods and development of new products (e.g. beta-thrombin, Factor IX); 3) comparison of human and bovine thrombin forms; 4) elucidation of the conversion mechanism and structure derivative thrombins (e.g., ordering cleavage steps, locating active sites Ser and His within cleaved chains, and searching for likely physiologic converting enzymes; 5) further comparisons of the properties and specificities of human alpha-vs. gamma-thrombin (e.g., synthetic compounds, fibrinogen, etc.); and 6) continued studies on the rate limiting enzymic steps of thrombins (e.g., binding vs. acylation). Major collaborative projects include: 1) completion of the amino acid sequence of human alpha-thrombin (A.R. Thompson, Seattle, WA, and H.S. Kingdon, Chapel Hill, NC) and limited sequencing of gamma-thrombin (D.A. Walz, Detroit, MI); 2) crystallographic studies on alpha-thrombin (R.M. Stroud, Pasadena, CA); 3) examination of conformational states of thrombins (L.J. Berliner, Columbus, OH, ad K.A. Koehler, Chapel Hill, NC); and 4) studies on thrombin reactions with platelets (T.C. Detwiler, Brooklyn, NY), antithrombin and heparin (R.D. Feinman, Brooklyn, NY), Factor VIII (H.R. Gralnick, Bethesda, MD), and Factor XIII (R.B. Credo, Evanston, IL). In addition to these, studies utilizing our thrombin preparations range from those of the complement system to induction of cellular transformations. BIBLIOGRAPHIC REFERENCES: Credo, R.B., Fasco, M.J., and Fenton, J.W., II. 1976. Activation of fibrinstabilizing factor (facto XIII) by human alpha- and gamma-thrombins. Fed. Proc. 35:648.